While organic electroluminescent (EL) devices have been known for over two decades, their performance limitations have represented a barrier to many desirable applications. In their simplest forms, organic light-emitting devices (OLEDs), also referred to as organic electroluminescent devices or as organic internal junction light-emitting devices, contain spaced electrodes separated by an organic light-emitting structure (also referred to as an organic EL medium) which emits light in response to the application of an electrical potential difference across the electrodes. At least one of the electrodes is light-transmissive, and the organic light-emitting structure can have multiple layers of organic thin films which provide for hole injection and transport from an anode, and for electron injection and transport from a cathode, respectively, with light emission resulting from electron-hole recombination at an internal junction formed at an interface between the hole-transporting and the electron-transporting thin films.
EL devices in recent years have expanded to include not only single color emitting devices, such as red, green and blue, but also white-devices, devices that emit white light. Efficient white light producing OLED devices are highly desirable in the industry and are considered as a low cost alternative for several applications such as paper-thin light sources, backlights in LCD displays, automotive dome lights, and office lighting. White light producing OLED devices should be bright, efficient, and generally have Commission International d'Eclairage (CIE) 1931 chromaticity coordinates of about (0.33, 0.33). In any event, in accordance with this disclosure, white light is that light which is perceived by a user as having a white color. Typical color combinations that produce white light are red, green and blue; blue-green and orange; blue and yellow but others are known.
Since the early inventions, further improvements in device materials have resulted in improved performance in attributes such as color, stability, luminance efficiency and manufacturability, e.g., as disclosed in U.S. Pat. Nos. 5,061,569; 5,409,783; 5,554,450; 5,593,788; 5,683,823; 5,908,581; 5,928,802; 6,020,078, and 6,208,077, amongst others.
Notwithstanding all of these developments, there are continuing needs for organic EL device components, such as yellow light-emitting layers, which will provide even lower device drive voltages and hence lower power consumption, while maintaining high luminance efficiencies and long lifetimes combined with high color purity. Such yellow light-emitting layers are useful for white light-producing OLEDs.
Commonly assigned U.S. Patent Application Publication No. 2008/0182129 discloses OLED devices with light-emitting layers containing an anthracene host, amino substituted anthracene dopants and can include additional dopants, including tetracenes.
U.S. Patent Application Publication Nos. 2009/0001874; 2008/0286445, and EP1182183 and WO2005029607 all disclose OLEDs where the light-emitting layers can contain anthracenes, amino substituted anthracenes and tetracenes among other materials.
U.S. Patent Application Publication Nos. 2005/0079381 discloses OLEDs with a light-emitting layer that contains a host, a light-emitting dopant and a first light-emission assisting dopant which is a tetracene. There may be a second light-emission assisting dopant which is an amine.
Diarylamino substituted 9,10-diarylanthracenes in OLED devices have described in U.S. Pat. No. 6,951,693, U.S. Patent Application Publication Nos. 2005/0153163; 2007/0134512; 2005/0260422; 2006/0127698; 2004/0209118; 2007/059556; and JP2003146951, KR2009046731, WO2007021117, WO2009061156, WO2009061145, WO2008013399, WO2007081179, and WO2007058503.
5,6,11,12-Tetraphenyltetracene (rubrene) derivatives where the phenyl groups are substituted are known as yellow emitters; see U.S. Pat. Nos. 6,387,547; 7,052,785; 6,613,454; U.S. Patent Application Publication No. 2005/0079381, and JP10289786.
However, these devices do not necessarily have all desired EL characteristics in terms of high luminance, low drive voltages, and sufficient operational stability. Notwithstanding all these developments, there remains a need to improve efficiency and reduce drive voltage of OLED devices, as well as to provide embodiments with other improved features.